Soluble 5'-nucleotidase is a critical enzyme for the regulation of the cellular nucleotide pool. It is important for hydrolyzing AMP to adenosine, a biologically active nucleoside, and the degradation of nucleotides to purine end products. This enzyme is altered in specific hematological diseases and is critical in determining which cells are susceptible to the accumulation of toxic metabolites in purine enzyme deficiencies associated with disorders of immune function. Our research has demonstrated the existence of two apparently distinctive soluble 5'-nucleotidases, "high Km" and "low Km" form, in cultured lymphoblasts and rat liver. Based upon our recent observations concerning 5'-nucleotidase, we propose to test the hypothesis that there are variable properties of 5'- nucleotidases which are related to tissue specific function, and these differences have a structural basis. To test the hypothesis, we will characterize specific forms of nucleotidase by purification and kinetic studies. To permit a new level of insight and extend our studies to other tissues, we propose the development of cDNA probes to assess mRNA levels and monoclonal antibodies to assess protein structure. Using these probes we will examine the T- and B-lymphoblast nucleotidases and compare the properties with the purified enzymes that we are currently evaluating. In addition, we will use our probes to examine tissue specific soluble 5'- nucleotidases, estimate the quantity of enzymes present, the molecular weight of the enzyme subunits, and the characteristics of the mRNA corresponding to these activities. The observations will be correlated with specific functions of these tissues. These studies will elucidate the molecular basis for nucleotidase regulation of nucleotide metabolism in normal and disease states. Ultimately novel therapeutic approaches may become available to manipulate adenosine release and nucleotide degradation to modify disease states.